Figure 1. The intrinsic fluorescence of eAPP_230–624.

A) Model of the eAPP_230–624 dimer derived from the SAXS model of eAPP_19–624 [18] illustrating the location of the tryptophans in eAPP_230–624 with respect to the dimerization interfaces. One monomer is shown in cyan and the second monomer is shown in blue. The surface corresponding to W338 is colored red. The corresponding residue in the blue monomer is on the back face, hidden in this view. The location of W546 and K624 cannot be precisely determined because of the low resolution of the model (20 Å). The two residues are located within the volume encircled by the dashed line. B) Emission peak of 0.64 µM eAPP_230–624 in PBS (black solid) and PBS containing 3.3% DMSO (black dotted) obtained with an excitation wavelength (λ_ex) of 295 nm using a Shimadzu RF-530PC spectrophotometer with a 4 ml quartz cuvette. For comparison, the spectra of 9 µM tryptophan in PBS (blue solid) and PBS-containing 3.3% DMSO (blue dotted) and 12 µM Aβ1-42 13-kDa oligomers in PBS (purple) are shown. C) Emission peak of 3 µM eAPP_230–624 in PBS obtained with an excitation wavelength (λ_ex) of 295 nm using a Spectramax XPS spectrophotometer (black). For reference, the emission spectra of 1–4 µM of tryptophan are also shown (grey). The peak shown is created by the design of the instrument, which displays reduced sensitivity as the wavelength approaches 360 nm.